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    <script type="text/javascript">
         
    //使用递归求到20的斐波那契数列之和
    //     function fibNumber(n) {
    //         if (n == 1 || n==0) {
    //          return 1;
    //         }
    //         return fibNumber(n-2)+fibNumber(n-1); 
    //     }
    //     console.log( fibNumber(20) );


    var count = 1;
    var a = 0;
    var b = 1;
    var c = 0;
    function fn(n) {
        c++
        n=a+b
        count+=n
        if(c == 20){
            return count
        }
        a=b
        b=n
        return fn(n)
    }
    console.log(fn());

    </script>
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